radius: Handle additional attributes

radius: Handle additional attributes

This allows radius plugin to handle additional radius attributes:

- Filter-ID (sets RADIUS_FILTER_ID env. var.)
- Framed-Route (sets RADIUS_FRAMED_ROUTE env. var.)
- Idle-Timeout
- NAS-IP-Address
- MS-Primary-DNS-Server
- MS-Secondary-DNS-Server
- MS-Primary-NBNS-Server
- MS-Secondary-NBNS-Server

[paulus@samba.org: Fixed formatting and simplified code making
 dns-1 and dns-2 default to each other, similarly wins-1 and wins-2]

Signed-off-by: Paul Mackerras <paulus@samba.org>